Hot gases pass through axial-flow turbomachines, in particular gas turbine plants for generating electrical energy, for driving the rotor-side turbine blading, which hot gases issue from the combustion chamber and subject all the walls enclosing the hot-gas duct and also components projecting into the hot-gas duct, such as vanes and blades for example, to extreme thermal loading. Due to the system and the design, the blades fastened to the rotor unit are provided in a plurality of blade rows which are arranged axially one behind the other and are at a respective axial distance from one another, which forms an intermediate space between two axially adjacent blade rows, and vane airfoils fastened on the stator side project into said intermediate space.
In regions of the rotor unit in which the rotor unit is radially surrounded by blades, the shroud bands lying radially on the inside on the blades prevent the hot gases which flow through the hot-gas duct from coming into contact with the rotor unit. Located in the regions between the blade rows for the thermal protection of the rotor unit are “heat shield elements”, which are arranged, as it were, like the blades in “heat shield rows”. Radially on the inside, the heat shield elements have a root contour, with which the heat shield elements are connected to the rotor unit, and have as heat shield a type of radially outer shroud band, which, via corresponding sealing contours, engages as far as possible in a gastight manner with the respective shroud bands of the axially directly adjacent blades.
Such an arrangement known per se can be seen from FIG. 2, which shows a partial longitudinal section through a rotor unit 1, to which blades 2, 3 of two axially opposite blade rows 2′, 3′ are connected. Provided so as to lie axially in between in the circular circumferential direction of the rotor unit 1 are a multiplicity of heat shield elements 4, the respective shroud band 5 of which leads axially on both opposite sides into corresponding sealing contours provided in the shroud bands 6, 7 of the blades 2, 3.
In order to prevent the heat shield elements 4 arranged in the circular circumferential direction from starting to wander in an uncontrolled manner in the circumferential direction relative to the blades due to rotation, at least the blade 2 shown in FIG. 2 provides a projecting “rectangular fastening lug” 11 radially on the inside below its shroud band 6 in the axial direction of the heat shield element 4, and this fastening lug 11, if appropriately positioned both in the axial direction and in the circular circumferential direction relative to the heat shield element 4, can be fitted into a clear intermediate space 13 which is defined by two projections 9, 10 of rib-like design which rise above a side wall section 8, facing the blade 2, of the heat shield element 4. Shown in FIG. 3 is a highly schematic partial plan view which shows the shroud band 5 of the heat shield element 4 in the axial direction of view, and extending under said shroud band 5 is the side wall section 8 which axially faces the blade and on which the two projections 9, 10 of rib-like design spaced apart in the circular circumferential direction u are provided. In the illustration shown according to FIG. 3, the fastening lug 11, which is of rectangular design in cross section and is firmly connected to the blade 2, preferably in one piece, is fitted within the clear intermediate space 13 defined in the circumferential direction u by both projections 9, 10.
For the case where the joined state shown in FIG. 3 between the fastening lug 11 of the blade 2 and the projections 9, 10 of the heat shield element 4 has been accomplished, it is ensured that all the heat shield elements 4 provided within the heat shield row are arranged in a rotationally fixed manner relative to the blades along the blade row 2′.
However, if the respective blade and the heat shield element axially opposite the respective blade are incorrectly positioned relative to one another as viewed in the circumferential direction u in the course of incorrect fitting, the case occurs where the fastening lug 11 provided by the blade 2 is not positioned in the region of the clear intermediate space 13 between both projections 9, 10 of rib-like design, but rather is positioned in the adjoining regions in the circumferential direction u, in which, however, there is no protection at all against rotational misalignment between the heat shield elements and the respective blades.
The spatial direction marked by the arrow in FIG. 2 indicates the removal direction −x for the blades arranged in the blade row 2′, the opposite direction, identified by +x, representing the fitting direction, in which the individual blades are pushed into the corresponding leading blade row along the rotor. A control wire K having a predetermined wire thickness serves in a manner known per se for the closure control once all the blades have been pushed axially into the blade row 2′, so that the wire K can be pushed through a suitable intermediate gap between two heat shield elements arranged in an adjacent position in the circular circumferential direction. It has hitherto been decided whether the fitting operation has been effected correctly or incorrectly depending on the push-in depth. However, it has been found that, even in the event of misaligned fitting of the projecting fastening lug provided on the respective blades and projections provided by the heat shield elements, corresponding positive closure control can be effected by means of the control wire. It is necessary to completely rule out this possibility.